This invention relates generally to improvements in a spinning rotor for an open end spinning machine, and more particularly to the prevention of the excessive accumulation of impurities in the spinning rotor.
As is known, the rotor for an open end spinning machine is generally provided with an annular wall surface which extends from the rim of an open end of the rotor radially outwardly from the rotary axis and downwards to a region of maximum diameter, where a fibre collecting surface is formed onto which the fibers are collected. Open end spinning machines employing the abovementioned rotors are widely in use for mass production of yarn and are required to be capable of continuous high speed spinning operation for a long duration. However, the spinning rotors in open end spinning machines are in fact supplied with separated fibers, which contain a certain amount of small impurities, such as dust, husks and the like. Even if such impurities entering the spinning rotor with the fibers are rolled into a yarn, there will be no influence upon the yarn quality, because critical impurities such as those causing yarn breakage have been removed before the fibers enter the spinning rotor, i.e., during the carding and drawing. However, the spinning rotor itself faces a serious problem which must be solved in order to allow it to continuously operate at high speed for a long duration.
In open end spinning machines, since the fibers are fed into the spinning rotor in the separated or opened state, the impurities mixed with the fibers can move in such a way that they are substantially released from restriction by the separated fibers. The impurities once separated from the fibers are difficult to re-mix with the fibers which have been deposited in the fiber collecting region of the spinning rotor in the form of a sliver or fiber ring, because of the difference in physical properties between the impurities and fibers. That is, the impurities generally have a greater mass than the fibers and therefore they are caused to move into the fiber collecting groove by the action of a centrifugal force stronger than that acting on the fibers, with the result that the impurities are deposited and accumulated in the region of maximum diameter or narrowest portion of the fiber collecting groove, while the fibers are positioned on the inner side of the impurities, i.e., on the side adjacent to the rotation axis of the spinning rotor. Therefore, when the fibers are removed by twisting them into a tail end of a yarn, it is difficult to cause the impurities on the outer side to be rolled in the twisted yarn especially where the impurities have a cubic shape. The impurities which thus remain in the region of maximum diameter of the fiber collecting groove are compressed by the strong action of centrifugal force and gradually develop, during a lengthly spinning operation, into a layer of deposition of considerable thickness due to the wedge-shaped configuration of the fiber collecting groove. This causes the radius of the maximum diameter region of the groove, i.e., the wedge's tip to become larger than the initial, most favourable radius. The fiber ring in the fiber collecting groove becomes expanded in width and is subject to less twisting action. This seriously affects the quality of the spun yarn and invites yarn irregularities, less yarn twist and decreased yarn strength.
It is of course essential for the high speed open end spinning to apply sufficient twisting action on the fiber ring, and therefore loss of twist due to the deposition of the impurities makes it difficult to carry out high speed spinning.
In view of these facts, there have been proposed various designs for a spinning rotor with a self-cleaning capability, which enables the impurities entering the spinning rotor with the opened fibers to be positively rolled in the sliver or fiber ring in the fiber collecting groove thereby removing from the spinning rotor. However, with the prior art designs, when it is attempted to decrease the amount of impurities accumulated in the groove, the strength of the spun yarn too is decreased, and it has been difficult to greatly decrease the amount of accumulated impurities while retaining yarn strength at or above a desired level.
U.S. Pat. No. 4,058,964 discloses one example of such prior art designs, wherein a fiber collecting groove is formed by two surfaces defining an angle of aperture of 45.degree. to 90.degree.. The bottom of the groove is of a radius of from 0.1 to 0.5 millimeters. Also, the biscator of the angle of aperture forms an angle with the plane of rotation of the groove of a value of from 0.degree. to 45.degree. while the yarn take-off direction forms an angle with the plane of rotation of from 0.degree. to 25.degree.. Although this spinning rotor can reduce the accumulation of impurities to a relatively low level, it involves the disadvantage that when the fibers in the groove are twisted into the tail end of a yarn being wound onto a package, they must be in frictional contact with a very limited portion of the bottom surface of the spinning rotor and therefore are oblidged to undergo strong abrasion resistance, resulting in an increased rate of yarn breakage, and production of a flutty yarn.
Furthermore, a spinning rotor as shown in FIG. 1 has been known, which has an inner surface 3 comprising a first frusto-conical portion 1 extending downwardly and outwardly, and a second frusto-conical portion 2 extending upwardly and outwardly to form a V-shaped groove 4 in cooperation with the first portion 1. In this spinning rotor of FIG. 1, since there is a large difference between angles .alpha. and .beta. which first and second fiber sliding parts 1a and 1b form respectively with the plane of rotation of the spinning rotor, when individual fibers first supplied onto the first fiber sliding part 1a reach the junction between the first and second parts 1a and 1b and are transferred to the second fiber sliding part 1b, they are obliged to undergo a rapid change in their travel direction and accordingly a relatively great shock, so that the fiber orientation or arrangement in the fiber collecting groove will be disturbed, resulting in reduced yarn strength.
Also, in this spinning rotor of FIG. 1, since the second frusto-conical portion 2 positioned below the plane of rotation of the maximum diameter portion of the groove 4 forms an angle .gamma. with said plane, the groove angle is greatly increased to the value .beta. plus .gamma. thereby increasing a possibility that the impurities and collected fibers in the groove 4 may be separated from each other, resulting in a decreased "rolling-in" rate of impurities into the fibers. Moreover, as is apparent to those skilled in the art, the collected fibers in the groove 4 are removed therefrom to form the tail end of a spun yarn 5, which is continuously taken up through a yarn take-up tube 6 from the spinning rotor. At that time, with the spinning rotor of FIG. 1, it is difficult to cause the impurities, which may present in the space defined between the yarn leading to the yarn take-up tube 6 and the second frusto-conical portion 2, or at least the space covered by the angle .GAMMA., to be rolled in the yarn, since the line, along which the yarn is removed from the groove 4 through the yarn take-up tube 6, is positioned considerably above the plane of rotation of the maximum diameter portion of the groove 4.
It will, therefore, be understood that, with the spinning rotor shown in FIG. 1, if the angle .beta. is designed to be of a relatively great value in order to increase the yarn strength, the amount of impurities collected in the groove will be greatly increased. In other words, it will not be possible to decrease the amount of impurities collected in the groove without decreasing the yarn strength.
It is accordingly a principal object of this invention to provide a spinning rotor for an open end spinning machine, which has a greatly increased self-cleaning capability so that the accumulation of impurities in the groove can be greatly decreased with the yarn strength maintained above the required level.